Abstract: A Pan-African orogenic unconformity between Cambrian and Ordovician and relatively complete Cambrian deposits were discovered in Xainza area, which is the only confessed Cambrian system in southern Qinghai-Tibet Plateau so far. This new discovery is not only an enrichment and complementarity of the stratigraphic system of Qinghai-Tibet Plateau, but also the only Pan-African orogenic unconformity between Cambrian and Ordovician in Qinghai-Tibet Plateau and its surrounding areas. The research on it can accurately determine the time limit of Pan-African movement and its geodynamic evolvement. This unconformity provides an unique sample to the study of the sedimentary process in northern Gondwana before Pan-African movement and has great and far-reaching significances to the research of the tectonic evolvement of Qinghai-Tibet Plateau.